art@ACC.ARPA (05/24/88)
>Someone was supposed to write up an RFC describing the mapping used for >class B and C addresses. What is currently being used in the cisco DDN X.25 >implementation is: > > class A: N.H.L.I > class B: N.N.H.I > class C: N.N.N.HI > >Where N represents the network number. H represents the PSN port number. L >is the logical host field and is still zero. I is the PSN number. For class >B addresses, the H field uses the unused L field. There are people out there using the logical host field on Class A nets. >For class C addresses, >the H field lies in the upper four bits of the last octet and the I field >in the lower four. We use pretty much the same algorithm in ACC devices except that we tend to us a 3 bit IMP number and 5 bit Port number split (since IMPs can support more than 16 hosts). > I don't know of anyone who has a class C PSN network. Unless BBN has done it, we probably are the closest. We actually have a Class C number that was assigned for use by our test IMP, but we have never really used it. Art Berggreen art@acc.arpa ------